Parison handling device

ABSTRACT

A parison handling device has a pair of opposed arms with each arm having at least a pair of grippers to selectively engage an extruded parison and transfer it to a second location such as to a mold of a blow molding machine. At least one gripper on each arm is both slidably and generally pivotally movable relative to the arm to facilitate initially engaging and gripping the parison and subsequent closing and stretching of a gripped end of the parison to more efficiently distribute the material of the parison such that after blow molding of the parison, the molded product has a substantially uniform wall thickness throughout. Preferably, a follower attached to each movable gripper is responsive to a profile or contour of a cam carried by each arm to guide the movement of the gripper corresponding to the profile of the cam. By adjusting or changing the profile of the cams, the slidable and pivotal movement of the grippers relative to the arm can be controlled to control the stretching of the parison and hence the distribution of the parison material as desired to form a particular product. By forming a product with a more uniform wall thickness, substantially less material is needed to form the product and therefore, the product may be formed at significantly lower cost.

FIELD OF THE INVENTION

This invention relates generally to forming hollow plastic products andmore particularly to an apparatus and method for handling a parison andtransporting the parison to a mold.

BACKGROUND OF THE INVENTION

Hollow plastic products such as some fuel tanks and similar products,have been made by an extrusion and blow molding process. In thisprocess, a molten plastic parison is formed by extrusion and thentransferred to a blow molding machine wherein a pressurized fluid isintroduced into the interior of the parison within the mold to force themolten parison into engagement with the interior walls of the mold. Whencooled and solidified, the molded plastic part will have an exteriorshape corresponding to the interior of the mold.

After extrusion and before being blow molded, the parison is hollow andhas a generally cylindrical or tubular shape. In some applications, suchas the production of automotive fuel tanks, the parison is large and mayhave a substantial length on the order of eight feet or longer. Duringtransfer of the parison from the extruder to the blow molding machine itis imperative to prevent the collapse of the parison wall upon itself tomaintain the hollow center of the parison in which the pressurized fluidis received to expand the parison within the mold.

Plastic products formed from prior blow molding processes have hadnon-uniform wall thicknesses with corners or other sharply contouredareas, and especially upper corners or contoured areas in the upperportion of the molded product, having substantially thinner wallscompared to other portions of the molded product. Thus, to ensure thatthese contoured portions and especially the upper corner areas of amolded product have at least a necessary minimum wall thickness, theother portions of the product must be formed with walls which arethicker than necessary thereby substantially increasing the amount ofmaterial and the cost to manufacture the product.

One device used to transfer a molten parison from an extruder to a moldis disclosed in Canadian Patent No. 2,135,544. In this '544 patent aparison carrying device has a collar which engages the parison after itemerges from the extruder and transfers the parison to a mold withoutpinching or collapsing of the parison walls. The collar has first andsecond halves which are made to grip the parison and which have fingerswhich are either fixed and hence, not movable, or which may pivot abouta fixed axis to enable the collar to pinch and close one end of theparison to permit an increased pressure to be developed within theinterior cavity of the parison. These fingers whether fixed or pivotedabout a fixed axis, do not provide any stretching or redistribution ofthe parison material and therefore, plastic products formed with use ofthis parison carrying device have the aforementioned problem ofnon-uniform wall thickness with upper corners and other contouredportions of the product formed with thinner walls than other portions ofthe product.

SUMMARY OF THE INVENTION

A parison handling device has a pair of opposed arms with each armhaving at least a pair of grippers to selectively engage an extrudedparison and transfer it to a second location such as to a mold of a blowmolding machine. At least one gripper on each arm is both slidably andgenerally pivotally movable relative to the arm to facilitate initiallyengaging and gripping the parison and subsequent closing and stretchingof a gripped end of the parison to more efficiently distribute thematerial of the parison such that after blow molding of the parison, themolded product has a substantially uniform wall thickness throughout.Preferably, a follower attached to each movable gripper is responsive toa profile or contour of a cam carried by each arm to guide the movementof the gripper corresponding to the profile of the cam. By adjusting orchanging the profile of the cams, the slidable and pivotal movement ofthe grippers relative to the arm can be controlled to control thestretching of the parison and hence the distribution of the parisonmaterial as desired to form a particular product. By forming a productwith a more uniform wall thickness, substantially less material isneeded to form the product and therefore, the product may be formed atsignificantly lower cost.

Each arm preferably has three grippers thereon with each of a pair ofmovable grippers disposed on either side of a middle gripper fixed tothe arm. Each movable gripper is driven by an actuator between retractedand advanced positions to facilitate engaging the molten parison andthereafter closing and stretching a gripped portion thereof. Desirably,when the arms are closed and the grippers are in their advancedpositions a generally hexagonal geometry is defined to increase thesurface area of engagement between the grippers and the parison.

Objects, features and advantages of this invention include providing aparison handling device which facilitates transfer of a molten parisonto a mold, prevents undesirable collapsing of the parison before it ismolded, stretches a molten parison before it is molded to moreeffectively distribute the material of the parison relative to the mold,enables a blow molded product having corner areas and other contouredportions to be formed with a substantially uniform wall thickness,substantially reduces the material needed to form a blow molded product,substantially reduces the cost to form a blow molded product, is readilyadaptable to form products of different shapes and sizes, is reliable,durable, of relatively simple design and economical manufacture andassembly and has a long useful life in service.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of this invention willbe apparent from the following detailed description of the preferredembodiments and best mode, appended claims and accompanying drawings inwhich:

FIG. 1 is a diagrammatic view of a transfer mechanism having a parisonhandling device embodying the present invention for transferring amolten parison from an extruder to a blow molding machine;

FIG. 2 is an enlarged diagrammatic view of the transfer mechanism andparison handling device of FIG. 1;

FIG. 3 is a perspective view of one arm of the parison handling device;

FIG. 4 is a top view of the parison handling device in a first positionwith the arms in an open position and the grippers in their retractedpositions and spaced from a molten parison;

FIG. 5 is a top view of the parison handling device in a second positionwith the movable grippers on the arms in their advanced positions andthe arms between their open and closed positions;

FIG. 6 is a top view of the parison handling device in a third positionwith the arms moved further towards their closed position with thegrippers advanced and engaging a molten parison;

FIG. 7 is a top view of the parison handling device in a fourth positionwith the arms moved further towards their closed position and themovable grippers being partially returned to their retracted position tostretch the parison;

FIG. 8 is a top view of the parison handling device illustrating thearms in their fully closed position with the movable grippers in theirfully retracted position to stretch, close and seal one end of theparison; and

FIG. 9 is a top view of a modified parison handling device having valvescapable of terminating the vacuum applied to the middle grippers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring in more detail to the drawings, FIG. 1 illustrates a parisonhandling device 10 attached to an arm 12 of a transfer mechanism such asa substantially automated robot 14 and manipulated by the robot 14 totransfer a molten plastic parison 16 from an extruder 18 to one of twoor more molds 20 wherein a product is molded into its final shape. Asbest shown in FIG. 2, the parison handling device 10 comprises a pair ofarms 22, 24 which are movable between open and closed positions toselectively engage and carry a parison 16. Three grippers 26, 28, 30 arepreferably carried on each arm 22, 24 with a pair of outer grippers 26,30 on each arm 22, 24 being movable relative to an associated middlegripper 28 preferably fixed to its associated arm 22, 24. As best shownin FIG. 3, each outer gripper 26, 30 carries at least one and preferablya pair of opposed followers 32, 34 each received in a separate one of apair of slots 36, 38 in opposed cam plates 40, 41 fixed to each arm 22,24 such that movement of each outer gripper 26, 30 is controlled by theprofile or shape of the slots 36, 38 in the cam plates 40, 41.Desirably, each outer gripper 26, 30 moves both slidably and generallypivotally relative to its associated middle gripper 28 to facilitateinitially engaging a parison 16 and subsequently stretching and closingone end of the parison 16 during manufacture of large hollow plasticproducts such as automotive fuel tanks to enable the fuel tanks, to bemade with walls of substantially the same thickness.

As shown in FIGS. 2 and 4-8, each arm 22, 24 is carried and moved by therobot 14 from a fully open position (FIGS. 2 and 4) with the arms 22, 24spaced from each other to a fully closed position (FIG. 8) with the armstogether. As best shown in FIG. 3, each arm 22, 24 may be an elongatepiece of channel iron having upper and lower walls 42, 44 and a mountingplate 46 at one end to connect the arms 22, 24 to a cross slide 45carried by an arm of the robot 14. A pair of protective guards or covers50 (FIGS. 4-8) are attached to each arm and extend on opposed sidesalong a plurality of conduits 52 which communicate a vacuum source witheach of the grippers 26, 28, 30. Preferably, a main vacuum line 54communicates the vacuum source with a manifold 56 which provides severaloutlets with one outlet for each conduit 52 which communicates with aseparate one of the grippers 26, 28, 30.

A pair of cam plates 40, 41 are preferably attached to each arm 22, 24with one cam plate 40 fixed to the upper wall 42 and the other cam plate41 fixed to the lower wall 44 of each arm 22, 24. Each cam plate 40, 41has a pair of generally longitudinal slots 36 and a pair of generallyarcuate slots 38 which guide movement of the movable outer grippers 26,30 both slidably or generally longitudinally and also generallypivotally relative to their arm 22, 24 and the middle gripper 28. Eachslot 36, 38 has a predetermined profile or shape to define and controlthe movement of the outer grippers 26, 30 through a specific path oftravel as desired for a particular application. The shape and locationof the slots 36, 38 may be changed to provide a different path of travelof the outer grippers 26, 30 as desired for a particular application.

Each of the grippers 26, 28, 30 is preferably carried by an arm 22, 24between the cam plates 40, 41 as best shown in FIG. 3. Each middlegripper 28 is preferably fixed to an arm 22, 24 with no relativemovement between them. Generally arcuate recesses 57 formed in themiddle grippers 28 provide clearance between the middle grippers 28 andthe adjacent outer grippers 26, 30 as the outer grippers 26, 30 aremoved relative to the middle grippers 28. A fitting 58 extending fromeach middle gripper 28 communicates a vacuum conduit 52 with an internalpassage 60 formed in the middle gripper 28. The passage 60 communicateswith each of a plurality of pockets 62 formed in the middle gripper 28and opening to an inner surface 64 of the middle gripper 28. The numberof pockets 62 formed in a middle gripper 28 can be varied as shown forexample, in FIG. 3 and FIGS. 4-8 wherein each gripper has two pocketsand three pockets, respectively. Preferably, to avoid adhering orsticking to the parison 16, each middle gripper 28 is formed of, orcoated with teflon.

Each outer gripper 26, 30 has two followers 32, 34 on each of a pair ofopposed faces 63, 65 with one follower 34 on each face 63, 65 slidablyreceived in an arcuate slot 38 and the other follower 32 slidablyreceived in a longitudinal slot 36 in each cam plate 40, 41. Desirably,each cam plate 40, 41 is generally symmetrical about the middle gripper28 on its arm 22 or 24 to provide a symmetrical movement of the outergrippers 26, 30 relative to the middle gripper 28. A fitting 70extending from each outer gripper 26, 30 communicates a conduit 52 withan internal passage 72 of each outer gripper 26, 30 which opens intoeach of a plurality of pockets 74 open to an inner surface 76 of theouter grippers 26, 30. Each outer gripper 26, 30 is preferably formed ofor coated with teflon to prevent the parison 16 from adhering to theouter grippers 26, 30. Each outer gripper 26, 30 has a generally arcuateportion 80 which cooperates with an adjacent recess 57 in a middlegripper 28 to facilitate pivotal movement of the outer grippers 26, 30relative to the middle grippers 28. Desirably, the arcuate portions 80are closely fit to the recesses 57 to prevent any significant gaps fromforming between the middle grippers 28 and the adjacent outer grippers26, 30 to prevent any parison material from entering between them. Asbest shown in FIG. 6, a rib 82 extending outwardly from an outer end 84of each outer gripper 26, 30 is constructed to cooperate withcorresponding rib 82 of an outer gripper 26, 30 on the opposing arm 22,24 when the outer grippers 26, 30 and arms 22, 24 are in an initialgripping position to pinch and seal any parison material extendingbeyond the outer grippers.

To move the outer grippers 26, 30 between their retracted position, asshown in FIGS. 2, 4 and 8, and their advanced position as shown in FIGS.3, 5 and 6, each outer gripper 26, 30 has an actuator 86 with anactuating rod 88 fixed at one end to the outer grippers 26, 30. Eachactuator 86 may be a pneumatic or hydraulic cylinder or some other powersource capable of reciprocating an actuating rod 88 between retractedand extended positions to move an associated outer gripper 26, 30between its retracted and advanced positions. Desirably, the actuators86 are pivotally carried by trunnions received in brackets 92 (FIG. 3)extending from and fixed to each arm 22, 24. The pivotal connection ofthe actuators 86 to the arms 22, 24 permits the outer grippers 26, 30 tomove both slidably and generally pivotally relative to the arms 22, 24when driven by the actuating rod 88 which moves essentially linearlyrelative to the actuator 86.

As each actuating rod 88 is moved from its retracted position to itsextended position, the outer grippers 26, 30 are moved along a path oftravel controlled by the followers 32, 34 within the slots 36, 38 of thecam plates 40, 41. Each longitudinal slot 36 permits an outer gripper26, 30 to slidably move generally laterally or longitudinally relativeto its arm 22, 24 and associated middle gripper 28. The movement of thefollower 34 in the arcuate slot 38 causes the outer end 84 of the outergrippers 26, 30 to pivot outwardly, away from its arm 22, 24, about theother follower 32 as the other follower 32 moves longitudinally in itsslot 36. Thus, the engagement and sliding movement of the followers 32,34 within their respective slots 36, 38 provides a compound motion ofthe outer grippers 26, 30 both slidably, in a longitudinal or lateraldirection, and generally pivotally relative to the arms 22, 24 andmiddle grippers 28.

OPERATION

To form a hollow plastic product, such as an automotive fuel tank, aquantity of polymeric material is melted and extruded to provide agenerally tubular, hollow molten plastic parison 16. Typically, plasticfuel containers have walls formed from multiple layers of differentpolymeric materials some of which provide strength and others whichreduce the permeation of hydrocarbon fuel vapors to the atmosphere. Forexample, some fuel tanks have an inner and outer skin of high densitypolyethylene with one or more layers of ethylene vinyl alcohol receivedtherebetween to provide a vapor barrier layer. Additionally, one or moreresin or adhesive layers may be provided between the vapor barrier layerand the skin layers to adhere them together.

To form such a fuel tank, the various layers of the fuel tank materialare co-extruded and emerge from the extruder 18 as a generallycylindrical, hollow multi-layer parison 16 open at its lower end 96 andupper end 98. As the parison 16 is emerging from the extruder 18 theparison handling device 10 is moved into position as shown in FIG. 4 forengagement with the upper end 98 of the parison 16 and each outergripper 26, 30 is moved by an actuator 86 to its advanced position, asshown in FIG. 5, such that each outer gripper is pivotally inclined andslidably longitudinally retracted relative to its adjacent middlegripper 28. With the outer grippers 26, 30 in their position, the arms22, 24 may be moved transversely toward each other by the lateral slides45 to an initial parison gripping position as shown in FIG. 6. Thelateral slides may be driven by a reversable stepper motor, pneumaticcylinder or other driving device through a pinion and rack arrangement.

In this initial gripping position, the ribs 82 of each outer gripper 26,30 on arm 22 cooperate with the ribs 82 of an opposing outer gripper 26,30 on arm 24 to pinch and seal any material between them and a generallyhexagonal cavity is defined between the grippers 26, 28, 30 of each arm22, 24. With a negative pressure or vacuum applied to each pocket 62, 74from the vacuum source through the conduits 52 and internal passages 60,72, the parison 16 is drawn outwardly in the direction of each gripper26, 28, 30 and into engagement with the inner surface 64, 76 of eachgripper 26, 28, 30 to prevent collapse of the parison 16 and to enabletransfer of the parison 16 from the extruder to a mold. The vacuumapplied through each pocket 62, 74 usually draws some of the parisonmaterial into each pocket 62, 74 creating projections extendingoutwardly of the parison 16 and into the pockets 62, 74 to improve thegripping and carrying of the parison 16 by the handling device 10. Thus,in the initial gripping position (FIG. 6), each gripper engages theexterior surface of the parison 16 and forms the upper end 18 of themolten parison 16 into a generally hexagonal shape. With each gripper26, 28, 30 engaged with the parison 16, the arms 22, 24 aresimultaneously moved downwardly (as indicated by arrows 97 in FIG. 1)away from the extruder 18 to break off or separate the parison frommolten material in the extruder and remove the parison 16 from theextruder 18. With the parison drawn outwardly by the vacuum communicatedtherewith through each of the six grippers, the parison 16 is removedfrom the extruder without pinching or closing off the upper end 98 ofthe parison 16.

After the parison 16 has been gripped and detached from the extruder 18,the robot transfers the parison to a mold 20 and the upper end 98 orneck of the parison 16 engaged by the grippers 26, 28, 30 is stretched,as shown in FIGS. 7 and 8, by simultaneously moving the arms 22, 24towards each other and moving the outer grippers 26, 30 towards theirpivotally retracted and longitudinally slidably extended positions ofthe outer grippers 26, 30 relative to the middle gripper 28. Thismovement of the outer grippers 26, 30 increases the longitudinaldistance between the vacuum pockets 74 of the outer grippers 26, 30 andthe vacuum pockets 62 of the adjacent middle grippers 28 to increase theperimeter length or circumferential extent of the upper end 98 of theparison 16 by stretching it. Desirably, this redistributes some of theparison material adjacent the upper end 98 of the parison 16 to provideadditional material for forming adjacent corner areas or contouredportions of the wall of the hollow product to enable the product to beformed with a substantially uniform wall thickness throughout.

After the parison 16 is delivered into a mold 20, it may be desirable toprovide a super atmospheric pressure within the interior of the parison16 to maintain its generally hollow shape and to prevent it fromcollapsing when transferred into the mold 20. To do this, as shown inFIG. 1, a needle 99 is typically inserted in the open lower end 96 ofthe parison 16 to provide a pressurized gas, such as compressed air,into the interior of the parison 16. Stretching pins 101 are alsoinserted in the open lower end 96 and are moved away from each other toengage and stretch the lower end 96 of the parison 16. After thisstretching, pinch plates 103, 105 are advanced towards each other topinch and seal the lower end 96 of the parison 16 with the needle 99remaining in the parison 16.

To permit an increased pressure to develop within the parison 16, theupper end 98 of the parison 16 must be closed. To close the upper end 98of the parison 16, as shown in FIG. 8, the arms 22, 24 are moved furthertowards each other to their fully closed position and the outer grippers26, 30 are moved to their fully pivotally retracted and longitudinallyextended positions. Notably, the movement of the outer grippers 26, 30to this position provides additional longitudinal sliding movement ofthe outer grippers 26, 30 away from the middle gripper 28 to furtherstretch the parison 16 as the upper end 98 is being closed. When theupper end 98 is closed, a low pressure (pre-blow) may develop within theinterior of the parison 16 to prevent the parison 16 from collapsing asit is placed into the mold.

After the molten parison 16 is received within a mold 20, opposed halves100, 102 of the mold 20 are closed and an high pressure (blow) isadmitted into the interior of the parison 16 to expand it outwardly intoengagement with the interior surface of the mold 20. After being blownoutwardly into engagement with the mold 20 cavity, the polymericmaterial is permitted to cool and solidify sufficiently such that whenit is removed from the mold 20, the molded part has and retains a shapecorresponding to the surface of the mold 20 cavity. The upper portion 98or neck and the lower portion 96 of the parison 16 which were pinchedtogether and closed prior to inserting the parison 16 into the mold 20may be machined off of the finished molded product.

As shown in FIG. 9, a valve 130 may be provided between the manifold 56and the middle gripper 28 of each arm 22, 24 to selectively provide thevacuum to the pockets 62 of the middle grippers 28. Desirably, when theouter grippers 26, 30 and arms 22, 24 are moved to close and stretch theparison 16 as previously described, each valve 130 may be closed toterminate the application of the vacuum to the parison 16 through themiddle grippers 28. Then, the parison material between the outergrippers 26, 30 on each arm can be stretched. Without terminating thevacuum applied to the middle grippers 28, only the material betweenmiddle grippers 28 and the adjacent outer grippers 26, 30 can bestretched (specifically, only the material between the outermost pocket62 of each middle gripper 28 and the immediately adjacent or innermostpocket 74 of the outer grippers 26, 30 may be stretched) with thematerial at and between the pockets 62 of the middle grippers 28 held bythe vacuum and prevented from stretching. This limits the amount bywhich the outer grippers 26, 30 can stretch the parison 16 withoutforming undesirably thin parison wall sections or tearing the parison16. With the addition of the valves 130, more material is available tobe stretched to avoid these problems.

By stretching the upper end 98 of the parison 16 with the slidable andgenerally pivotal movement of the outer grippers 26, 30 relative to themiddle grippers 28 and arms 22, 24, the material of the parison 16 canbe better distributed to enable blow molding of a part having asubstantially uniform wall thickness throughout. Notably, significantlyless material is required to form a product as material can bedistributed to areas of a parison which will subsequently form uppercorner areas or contoured portions in the upper portion of the finalmolded product to ensure the final product will have a sufficient wallthickness at these upper, contoured areas. Thus, excess material is notneeded for the remaining portions of the plastic product which can thusbe made thinner and more uniformly. Thus, the cost to manufacture eachplastic product is dramatically reduced because of the decreased amountof material which is used to form the final product and which must beprocessed for each product. In use of one embodiment of the handlingdevice, the volume of material needed to form a fuel tank was reduced byabout 10-15% providing a substantial cost savings both in material andprocessing to melt and extrude the parison and mold the parison into afuel tank.

What is claimed is:
 1. A parison handling and carrying device,comprising: a pair of arms with at least one arm movable towards andaway from the other arm to permit selective engagement with a parisonhaving a tubular portion received between them and carrying of theparison; at least one cam carried by each arm and having a profile; atleast two grippers carried by each arm with at least one gripper on eacharm being movable relative to the arm between advanced and retractedpositions to vary the longitudinal distance between at least a pair ofadjacent grippers; at least one follower carried by at least one movablegripper of each arm with each follower being responsive to the profileof an associated cam to control the movement of its associated movablegripper; and a separate actuator carried by each arm and operablyconnected to each movable gripper to move the movable grippers betweentheir advanced and retracted positions, whereby when displaced by anactuator the engagement of a follower with a cam determines the path oftravel of said movable gripper with the path of travel relative to thearm increasing the longitudinal distance between at least a pair ofadjacent grippers constructed and configured to stretch the material ofa parison received between the grippers and to close the tubular portionof the parison received between the grippers as the arms are movedrelatively toward each other for carrying and handling the parison. 2.The handling device of claim 1 wherein each movable gripper whichcarries a follower moves both slidably and pivotally relative to itsarm.
 3. The handling device of claim 1 which also comprises at least onevacuum pocket formed in each gripper and constructed to apply a vacuumsource to a portion of the parison engaged by the gripper to draw andhold the parison onto the gripper.
 4. The handling device of claim 1wherein when the grippers are in their retracted positions they arealigned with each other and with the arm and when the movable grippersare in their advanced positions the movable grippers are inclinedrelative to each other and at an angle from the arm.
 5. The handlingdevice of claim 1 wherein each cam is a cam plate with at least one camplate carried by each arm and with the profile of each cam defined in aslot formed in a cam plate with each follower received in a slot tocontrol the movement of the movable grippers.
 6. The handling device ofclaim 5 wherein each movable gripper carries a pair of followers andeach cam plate has one slot for each follower of a movable gripper. 7.The handling device of claim 6 wherein each cam plate has a first slotextending longitudinally of the arm and a second slot which spans an arcto control the pivotal movement of a movable gripper relative to thearm.
 8. The handling device of claim 4 wherein three grippers areprovided on each arm with a pair of movable grippers disposed on opposedsides of a middle gripper fixed to the arm.
 9. The handling device ofclaim 8 wherein when an arm is moved towards the other arm to engage theparison and the movable grippers are moved to their advanced positions,a hexagonal opening is defined between the grippers of each arm.
 10. Thehandling device of claim 8 wherein when the movable grippers are movedfrom their advanced positions to their retracted positions, they moveslidably away from the middle gripper while also moving pivotally. 11.The handling device of claim 1 wherein each movable gripper has a ribextending therefrom constructed to cooperate with a rib of a movablegripper of an opposed arm to pinch and seal any parison material betweenthe ribs when the arms are moved into a position to engage an objectbetween them.
 12. The handling device of claim 8 which also comprises atleast one vacuum pocket formed in each gripper and constructed tocommunicate a vacuum source with a portion of the parison engaged by thegripper to draw and hold the portion of the parison onto the gripper anda valve disposed between the vacuum pockets of each middle gripper andthe vacuum source to control the application of the vacuum from thevacuum source to the middle grippers.